1. Field of the Invention
This invention relates to a powder of lead-containing oxide for the production of an element for electrical, electrochemical and other various uses, and a process for preparing the same. This invention also relates to a sintered body and an element prepared from the lead-containing oxide powder.
2. Related Art Statement
There have been known, in the art, a variety of lead-containing oxide which may be used as dielectric materials having high dielectric constant; piezoelectric materials and a collector in electrical application. Accordingly, it is necessary to provide a powder of lead-containing oxide, which can be easily sintered to give a high density sintered article at a relatively low temperature and a process for preparing the powder.
It has been known that sintering of such a material may be accerelated by increasing the content of lead in the material to be sintered. (In this connection, reference should be made to "Research on Sintering of PbO and PZT", reported by Osamu Yamaguchi in "Powder and Powder Metallurgy" ("FUNTAI OYOBI FUNMATSU YAKIN"), Vol. 17, No. 3, Page 116.)
The prior art technology referred to above and disclosed by the preceding reports including Yamaguchi's article relates to a so-called liquid phase sintering mechanism wherein sintering is promoted or accelerated by the addition of lead oxide in an amount in excess of 10 to 60% of the stoichiometric quantity due to the presence of liquid phase of excess lead oxide during the step of sintering zirconium titanate. However, this known process has a disadvantage in that the excess lead oxide is left in the resultant sintered body to affect adversely the electrical or mechanical properties of the resultant products. The liquid phase sintering process has another disadvantage in that gas bubbles are hardly expelled from the molded mass during the sintering step since the mass under sintering, in general, abruptly shrinks at the initial stage of sintering. As a result, gaseous materials are enclosed in the sintered body to form an enormous number of minute voids in the product to lower the density thereof. This problem is not limited only to the production of a sintered body of zirconium titanate, but is commonly found in the preparation of a sintered body from a lead-containing powder by the conventional technology, particularly by the liquid phase sintering processes.
Another known process for producing a lead-containing oxide powder is a so-called solid phase calcining process wherein a powder composition containing lead oxides, metal oxides and metal carbonates is prepared to have a desired composition followed by calcination, and then the calcined body is pulverized and the pulverized powder is calcined again, the calcination and pulverizing cycles being repeated until a calcined body having desired properties is obtained. However, the resultant lead-containing oxide powders by the conventional solid calcining process have a disadvantage in that they must be sintered at a high temperature with an attendant excessive growth of powder particles to result in increase in average diameters thereof. The density of a sintered body prepared by the use of such a powder of large average particle size is low.
It is also known in the art that lead-containing ceramic elements, such as laminated ceramic condenser elements, or bimorph type or laminated type actuators, may be produced from a lead-containing oxide powder. Such an element for electrical or other various applications may be produced by a process wherein a lead-containing powder is mixed with an organic binder and other additives to prepare a mixture which is molded, and then a material for electrodes is printed or otherwise applied on the molded mass and is pressed at a temperature of about 100.degree. C., followed by baking at a temperature of higher than 1200.degree. C. However, since a molded mass of lead-containing oxide and a material for electrodes are baked at a high temperature, when a conventional lead-containing powder is used, the material for electrodes is limited to high melting point metals, such as platinum, rhodium, palladium and iridium, or alloys thereof or tungsten. As known, these metal materials are not only expensive but also high in electrical resistivity, and thus they are not adapted for use in high speed electronic circuits or high density electrical equipment or integrated circuits.